The present invention relates to methods for joining living tissues, including veins, arteries, microvessels, tubes, nerves, organ tissues and biological surfaces, such as peritoneum, omentum, fascia, shin, artificial tissues, and to pharmaceutical products useful in joining these tissues.
Joining tissues such as veins, arteries, microvessels, tubes, nerves, tissues and biological surfaces such as the peritoneum and skin has mainly been carried out clinically to date by suturing and microsuturing.
Microsuturing requires considerable skill and is a time consuming procedure. Frequently, tissues which have been joined by microsuturing form considerable scar tissue. Some of the difficulties encountered with microsuturing can be better understood by considering the example of rejoining damaged peripheral nerve tissue.
Peripheral Nerves
The electrical signals that control the body""s organs and transmit information back and forth to the central nervous system (CNS) travel along peripheral nerves. The structure of these peripheral nerves is analogous to telephone cables. In a telephone cable there is a strong protective outer coating that protects all the inner components. The copper wires are often grouped in separate insulating tubes that lead to different systems. Each of the inner copper wires is a single line that can transmit electricity in either direction and has an insulating coating around it so that it does not interfere with the lines next to it.
A peripheral nerve (FIG. 1) has an outer membrane consisting of connective tissue such as collagen. This membrane (epineurium) protects and holds the separate nerve bundles together. The nerve bundles which lie inside this membrane are called fascicles. These fascicles also have a collagen based surrounding membrane and their task is to group together nerve axons supplying a similar area of the body. Inside the fascicle membrane the axons are surrounded by loose connective tissue. The axons are a long extension from a cell body which is contained within the CNS in the spine or the brain. Sensory axons transmit to the CNS and motor axons transmit from the CNS. Nerve metabolism is sustained by the vascular system from both outside the nerve and along the centre of the nerve.
Peripheral nerves can have very small diameters. For instance, the mature median nerve at the wrist is approximately 1 cm in diameter and contains an average of forty fascicles, each of which can contain up to 4500 axons. When a peripheral nerve is cut all axons distal to the wound change their properties as axon flow is cut off from the cell body. Even when the nerve is reconnected, these axons continue to degenerate distally. The Schwann cells which normally wrap themselves around the axons as insulation guide regenerating axons. Joining nerves as accurately as possible by lining up corresponding fascicles enables the axons to more efficiently regenerate.
Operating upon nerves has been facilitated by using magnification and special microsurgical equipment. Accurate repairs need to be effected at the fascicular level ensuring that regeneration is along the correct bundle leading to the original area those axons supplied. The current technique of peripheral nerve repair uses microsuturing (FIG. 2). This technique requires a dedicated, trained surgeon as microsuturing of just one of the many fascicles with three or more microsutures (using say a 70 micron diameter needle and 30 micron thread) can take very long operating times.
Microsuturing is at present clinically used where the skills are available. Unfortunately, there are relatively few surgeons who have the necessary manipulative skills for operating at high magnification. Even a reasonable microsuturing technique results in long operating times with added damage to the inner axons due to sutures penetrating the thin insulating perineurial sheath. The use of sutures results in some scarring of the repair due to foreign body reaction. There is also evidence which indicates that in the long term scar tissue formation and scar maturation can lead to impairment of the joined nerve.
Work has been performed on the use of lasers alone in effecting nerve joins. One of the problems of laser welding has been the fact that the intact gel-like nerve tissue of the axons is actually under pressure within the fascicle. When the fascicle is cut this material extrudes. This can lead to the direct laser weld being formed on nerve tissue rather than the surrounding membrane of the fascicle, causing nerve damage. To date the welds have typically been made using infrared lasers such as CO2 lasers which rely on water absorption for energy transfer. Tissue preparation before welding relies on overlapping the nerve membranes. This is difficult due to the extruding gel-like axons and so can lead to denaturation of the nerve axon material. The affected tissue tends to scar and the fibrous tissue that proliferates as a result is a poorer electrical conductor than nerve tissue. The bonds formed to date as described in the prior art using laser welding have typically lacked strength. These laser joins alone tend to fail so microsuturing has been used in addition to welding to strengthen these joins.
To deal with at least some of the deficiencies of laser welding, various glues have been used in forming the welds. These low protein concentration, fluid glues tend to run between the ends of the nerve that are being joined which may result in damage to the axoplasm of the nerve fascicle and also hinder regeneration. They are also applied around the join which is then circumferentially welded. These joins later show thick scarring which causes stricture of the nerve. Moreover, the joins tend to be weak.
The welding techniques so far available also tend to lack precision. Factors that influence the precision of this approach adversely include differences in: the consistency of the glue used; the aperture of the needle or other device used to apply the glue; and the pressure exerted in applying the glue.
The present invention provides a method for joining tissue comprising:
aligning and abutting edges of the tissue to be joined;
applying a solder, across the aligned and abutted edges; and
exposing the solder to an energy source under conditions which provide a transfer of energy from the source to the solder to cause the solder to bond to the tissue surface adjacent the edges thus providing a weld holding the edges together.
In addition to causing the solder to bond to the protein of the underlying tissue, the energy transfer can affect the structure of the solder itself leading to bonding within the solder and an enhancement of the strength of the solder and hence the join.
Drops of solder are typically used where the solder is a fluid solder, and are xe2x80x9cpaintedxe2x80x9d across the edges.
The solder can also be provided as a preformed solid strip.
The energy source is typically a laser.
A variety of tissue types can be joined using this method. The method is applicable to anastomoses of biological tubes including veins, arteries, lymphatics, nerves, vasa efferentia, fallopian tubes, bile ducts, tubes of the alimentary canal, the ureter, the urethra, tear ducts, bronchi and any other such bodily tubes as well as to repairs of incisions or tears of biological organs such as kidneys, liver or spleen, or of biological surfaces such as the peritoneum and skin. It will therefore be understood that the method can be used in a variety of join situations including the joining of cylindrical anastomoses and the closure of linear defects such as incisions.
Where the tissue repair is with respect to nerve tissue or other tissue tubes where the tube contents need to be protected from damage, it is especially important that the weld should not be concentrated on the edges being joined as this can damage extruded tissue. Rather, the weld should be distributed across the planar or tubular surface in which the discontinuity lies.
Where the tissue to be repaired is an essentially hollow body tube such as a blood vessel, the repair can additionally comprise the insertion of a thin-walled hollow cylinder of solder inside the tube under repair so that the cylinder spans the severed portions of the tube. Typically, while the severed tube and cylinder assembly is held together, energy from the energy source is directed through the tube wall to bond the cylinder to the tube ends. The cylinder may incorporate a dye, as hereinafter described, to attract energy to the cylinder for more efficient welding. The repair is completed by the application of at least one strip or drop of solder across the edges on the outer surface and treating the applied solder as described above.
Where the repair is with respect to tissue surfaces such as peritoneum, it will be understood that it is less important to avoid concentration of welding on the edges.
The method can also be modified for the repair of other discontinuities in tissue surfaces such as holes, resulting from accident or surgery. In this form of the invention the solder may be spread or pre-cut to conform to the shape of the repair site, and the edges of the repair site may not need to be aligned or abutted for the repair to be effected.
A typical nerve repair using the method of the invention is one in which the edges are ends of a cut peripheral nerve fascicle that are to be joined together or an end of a nerve fascicle and the fascicle of substitute nerve graft material. This latter situation is particularly applicable where nerve repair is required but a section of the nerve under repair has been severely damaged or is unavailable, so that the available ends of the fascicle are too remote from each other to be directly joined. The actual nature of the damage sustained by the nerve and whether the repair is a primary or secondary repair are factors affecting recovery but in any case the edges of nerve fascicles to be joined are cleanly cut at right angles prior to joining.
Application of the solder as a strip or strips, with space between for natural co-aptation of the surfaces themselves permits the nerve under repair to revascularise. Circumferential welding, by comparison, can inhibit the body""s natural healing process and so slow down blood capillary access needed for the area of repair. Laser soldering and suturing techniques ultimately rely on the body regenerating connective tissue to hold the nerve together after either solder or suture connections break down and are replaced by the healing process. The present inventors have shown in vivo experiments that successful regeneration can be achieved by the methods of the present invention without restriction on surrounding tissue movement after the operation. In the case of nerve repair operation on human patients it is routine to initially restrict the movements of the joints of the operated limbs to assist in reducing tension across the repair site.
Typical biodegradable, biological solders useful in the method of the invention include protein solders.
It is envisaged that other naturally occurring biomolecules could be used as alternatives. Further analogues of biological, biodegradable polypeptides could be used. Analogues of biological, biodegradable polypeptides useful in the invention include synthetic polypeptides and other molecules capable of forming a viscous xe2x80x9cgluexe2x80x9d that does not react adversely within the tissue undergoing repair.
The protein solder may be a solid or a fluid solder composition.
Fluid protein solder compositions useful in strip welding typically comprise between 100 and 120 mass % of protein relative to water. Preferably, fluid protein solders comprise between 100 and 110 mass % protein relative to water.
The fluid solder strip is typically 50 to 200 xcexcm in thickness. Its length is selected to suit the join to be formed but typically is of the order of 2 to 3 mm in length. It is typically painted across the join.
Solid protein solder compositions useful in strip welding typically comprise between 120 and 230 mass % protein relative to water. Preferably the strip comprises 170 to 230 mass % protein and more preferably about 210 mass %.
It will be understood that different proteins will have different degrees of solubility in water or appropriate solutions which in turn will affect the optimum concentration of protein in the composition for different protein solders. Appropriate ranges for particular proteins in both solid and fluid solders can be determined based on the known properties of the proteins.
Typically, the solid protein solder composition is provided as a preformed strip. Solid solder strips are easier to manipulate than fluid solders. Under the moist conditions inherent in surgery fluid solders may run making it difficult to laser denature the solder before it has spread. The solid solder strips can have a paste like or more rigid consistency. They are typically placed across the join with microforceps. In one form of the invention, it is envisaged that the solder strips will be substantially rectangular in shape. However, different shape strips may be required in different repair situations. It may also be desirable to provide a plurality of strips joined together for efficient repair of a large or a substantial number of repair sites.
The protein solder may comprise a single protein of which albumin is a typical example or alternatively the solder may comprise more than one protein.
Albumin has desirable qualities for solid solder strip formation since it has a high proportion of xcex2 sheet structure which gives rigidity to the strips. Fibrin is another example of a protein with significant xcex2 sheet structure. Incorporation of xcex1 helical protein in the solder can assist in making the strips more malleable and thus retain a flatter profile which is particularly well suited for joining nerve ends. An example of a suitable proportion of xcex1 helical protein is between 1 and 10% by weight of the protein used. About 5% is a preferred amount. Collagen, tropoelastin and elastin are examples of suitable a helical proteins.
Protein used in the solder is selected to minimise the risk of adverse host reactions and should therefore preferably be an autologous protein for the host or a foreign protein of low antigenicity.
The proteins may be obtained from any suitable source. Recombinantly or synthetically produced proteins as well as purified naturally occurring proteins may be used.
Preferably, when the solder is to be used with a laser which produces energy at a suitable wavelength the composition includes a substance, such as a dye, which absorbs energy at the wavelength produced by the laser with which the solder is to be used. It is preferable to choose the combination such that the dye or other substance absorbs the energy transmitted by the laser efficiently but the underlying tissue to be joined absorbs the transmitted energy poorly. The dye or other substance assists in making the welding specific to the solder used which in turn assists in minimising accidental tissue heating damage to the underlying tissue.
The process of bonding, where protein solders are used, relies on protein molecules being available for cross-linking. This occurs when the protein molecules are unfolded. Upon laser irradiation of, for instance, an albumin and indocyanine green containing solder at a nerve tissue join, albumin molecules are heated through energy transfer from the indocyanine green molecules, allowing them to unfold and bond between themselves and to neighbouring tissue surface such as the fascicle membrane.
Dyes which contrast with the tissues being repaired can also be useful in making the solder easier to see. An example of a dye with this property is indocyanine green.
When the laser used is a CO2 laser, a dye will not assist the energy transfer, as the energy transfer is by water absorption.
The energy provided by the energy source should be sufficient to bond the solder to form the weld while minimising damage to the underlying tissue. The temperature required to denature a protein solder is typically at least 50xc2x0 C. and may exceed 100xc2x0 C. A preferred range is 50xc2x0 to 90xc2x0 C. A particularly preferred range is 80xc2x0 to 90xc2x0 C.
The time of treatment for each join to be effected can vary depending on such factors as ambient conditions, altitude, and of course the nature of the tissue to be joined. The duration of treatment is typically short. A 30 second passage for laser treatment of a 0.4 mg strip is an example of the time involved although it will be understood that shorter or longer treatment times could be required. It will be understood that solid solder takes longer to denature than fluid solder.
In a second aspect the present invention provides a protein solder composition comprising protein and a suitable solvent for the protein. Water is typically used as the solvent for water soluble proteins.
In a third aspect the present invention provides a kit for use in joining tissues comprising, in a preferably sterile pack, a plurality of protein solder strips and/or shapes of the second aspect of the invention. Preferably a plurality of strip lengths and/or shape sizes are included in the pack.
The kit preferably includes means for sterile manipulation of the strips. The kit also preferably includes means for measuring the strips.
The kit may also comprise an energy source such as a fibre coupled laser system.